Variable warp airfoil



Feb. 5, 1952 l. B. BENSEN VARIABLE WARP AIRFOIL Filed June 27, 1946 Invent-Joh: Igor B. Rensen, [M i. 7&4

H i s Attorney present invention, the reversible electric motor driven flexible shaft 23 is connected through suitable power gearing, preferably in the form of a worm 31 and worm gear 38 to rotate the innermost rib 28 of the blade about the warp axis provided by the spar I4. As shown the worm 31 is rotatably mounted in a yoke extension I'Ia of the pitchfcontrolf'arm I1 and vthe worm gear 38 is rotatably mountedi'on spar VIli and rigidly connected through the collar 39 and the rein- J the finger 44 extending l.between the adjustable .l

stops 45l and 46 vcarried in suitable brackets 41 and 48 e'axtendingffro'rn.theiplate,4I;I A pair of .warpcontrol elements or tubes 50 and I .spaced apart on' opposite sides of the spar 'I4 extend through each of the transverse ribs-"of the blade. I3and are interconnected rigidly to the outer endof the spar I4 by means ofthe rigid tip. of the blade 36. The inner ends of the two spaced apart warp control elements orv tubes 50 'and 5Iv are mounted securely inthe S reinforcing plate-40 to be rotated about the axis ofv vspar I4 by means Vof the worm gear 38.

` As shown-more clearly in Fig. 3 provision is made for xedly securing each of the transverse ribs of blade I3 to the spaced apart warp control elements 50 and 5I so as to bias the blade to a predetermined configuration when there is no twisting force exerted by means of the worm gear 38. Wherembothpositive and negative twisting of the blade is required, the predetermined position just noted is preferably intermediate the maximum positive twist and the maximum negative'twist and may be such that the blade has zero twist or warp. v To accomplish this result the two warping tubes `SEI-'and 5I are provided respectively with the drums 52 and 53 of considerably increased diameteneach of which preferably is Welded to .the'corresponding tube. The drum 52 is" clamped between the two split jaws 54 and 55 formed at the end of thewarp. control plate 4I when the clamping screw 56 is tightened. In a similar manner drum 53 is clamped between the jawsr5l and 58 when the clamping` screw 59 is tightened. Thus in manufacturing the blade, the rib 28 can bemounted on the axial spar I4 in proper Aalignment with the rigid tip 36 to provide zero blade twist. .Thereupon the clampingscrews 56 and 59 are tightened to enable the torsional resiliency ofelements 50 and 5I to bias the rib 28 to such predetermined aligned position.

In order to provide for the necessary relative longitudinal movement between the trailing edge portions of the bladelenvelope 21 during the warping or twisting of the blade I3, each of the series of 4-ribs- 28-35 .is provided with the longitudinal slit 6'0- terminating in the opening 6I and having a laterallyextending portion 62 to permit relativev sidewisemovement Ybetween the opposite halves ofeach ribV 28-35 at-the trailing edge thereof. 'I he forward ends-of the ribs are tied together by means ofa'combing strip 65 and the two cooperating-trailingedge combingstrips 66 and 61 serve to interconnect'the trailing endsL of theseries4 of ribs on opposite'sides of the longitudinal slit 68; `By'means ofthis construction the combing strip 66 is enabled to move sidews'e relative to the combing strip 61 due to the inherent resiliency of the material of which the ribs are formed. The upper portion of the blade envelope 21 is carried over the trailing edge of the combing strip 66 and fastened thereto adjacent one side of the lateral slot 62 by riveting or in other suitable manner. 'Similarly the lower portion of theblade"v envelope 21 is secured to the relatively movable lower portion of the ribs 29 adjacent the opposite side of the lateral slot 62. Separation of the two combing strips 66 and t1 is prevented by suitable means such as the groove 1i! formed in the upper combing strip 66 and the tongue 1I extending from the lower combing strip 61 so as to permit longitudinal relative movement of the jtwo but resisting separation thereof.

The manufacture of the blade is facilitated since the individual ribs each may be clamped to the `warp control tubes 5D and5I with each rib in predetermined alignment with the tip 36 of the blade even aftery the twistable airfoil shaped envelope 21 is applied. Thisy is accomplished by providing suitable small openings 'i3 and 'i4 in the blade enve1ope21 to permit access to the clamping screws 56 and 51. of each` rib is obtained, the access'openings 13 and 'I4 may then' be'suitably sealed. Likewise similar access openings 15 and .16 .areprcvided in the twistable blade envelope 21 to permit access to the adjustable stop 45 and 46. vvhich,by their engagement with the warp control finger 44 carried by spar I4 serve to limit the angular movement of each rib in each direction relative to the spar. Thus when the manufacture of the blade is completed, the exact angular movement permitted each transverse rib'ofthe blade in each' direction from the biased intermediate position can be predetermined in order to provide. a desired maximum positive twist and .also a desired maximum negative `twist from thefintermediate zero ltwist position. With the stops on the successive ribs set progressively closer together from root to tip of the blade, a desired retrogressive twisting of the blade is insured'fromroot to tip when the reversible electric warp control motor 40 is energized to operate through the Worm 3'I and worm 38 to apply a powerful twisting force to the innermost rib 28. This. powerful twisting force is transmitted through the reinforcing plate 4E to the spaced apart warp. or twist control elements 50 and 5I with the force exerted thereon providing a combined torsional and bending moment. As a result the innnermost rib will be rotated lon spar I4 the maximum amountland each succeeding rib be rotated a lesser amount corresponding to the adjustment of the stop screws45 and 48 thereof. As the blade envelope 21 is, thus twisted, a relative movement of the combing strips A66 and 61 at the trailing edgeof the vblade `occurs and thus avoids thel building, up of excessive strains in the blade envelope thatmight cause wrinkling or crimping thereof. i p l The improved variable. warp blade of the vpresent invention is particularlyVY adapted for use on an aircraft of the vertical lifttypedisclosed in a concurrent application, Serialllo: 619,652, filed June 27, 1946, in the. name of D. C. Prince and assigned Vto the .saine .assignee as the present invention. .Certain variable warp, Y,variable pitch blade structures andA :associated control mechanisms suitable for :this .convertible flight type aircraft form a portion ofthe subject matter ofthisfrince applicationL Myzpresent inven- After proper alignment k aircraft hanging on the propeller.

tioncomprises improvements in such blade structures and :control mechanism. In this type of aircraftA both the blade pitch and twist .must be reversed correspondingly. Thus vthe blade must be given a slight vpositive pitch anda positive twist in order to provide thrust for vertical ascent of the aircraft like a helicopter with the Y when sumcient .altitude is gained, both the blade pitch and warp are then reversed in order to drive the aircraft at high speed in horizontal iiight. To accomplish this result the pilot must yoperate the variable blade `pitch control vmechanism to provide a desired pitch and at the same time operate the manual warp control switch 99 to energize the warp control motor 2|3to provide the proper warp for aerodynamic efiiciency. Upon rotation of motor 29 in one direction, the worm wheel 38 vvwill be rotated -to twist the blade |3 until the corresponding stops serve to limit the rotation of f each transverse rib to provide the proper blade twist required to obtain the maximum aerodynamic eiciency of the blade at the correspending pitch. When the blade pitch is to be reversed, the manual switch 99 then is thrown in the opposite direction to reverse the direction of rotation of the Warp control motor 29. ThereuponV the blade |3 will be twisted in the opposite direction to the full extent permitted by the stops carried by each rib.

As indicated in Fig. 4 suitable automatic limit switch -mechanism 8| may be provided in the motor circuit for deenergizing the motor 29 after each twisting and untwisting of the blade i3 is accomplished. comprises in the preferred form shown a switch base member 9.2 mounted directly upon the blade supporting spar I4 so as to remain stationary when the rib 29 is rotated on the spar I9. The switch base member 9-2 carries the three normally spaced apart resilient switch contact arms 84, 85, 99 Ywith the center arm 85 extending between the two actuating pins 81, that are carried by the rib 28. The' normally closed limit switches 99 and 9| also are adjustably mounted upon rib 28 so as to move therewith upon rotation .of the rib to selectively engage with the stationary switch base member 82 and thereby eifect the opening of the corresponding limit switch upon a predetermined rotation of the rib 28 in each direction.

Alin operation when the manual warp control switch 80 is moved out of engagement with its middle contact 95 as shown in Fig. 4 and into engagement with its right hand contact 99, a circuit is established for energizing the motor 29 to rotate the rib 29 in a clockwise direction about the spar ki 4 from the position in which it is shown in Fig. 4. This circuit may be traced from the battery B through conductor |99, manual selective switch 89, contact 96, conductor |9|, limit switch 9|, conductor |92, the clockwise rotation eld winding |93 of motor 29, conductor |99, the armature of motor 29 and conductor |95 through battery B. As soon as the motor 29 has rotated rib 29 the required amount to engage the successive ribs with their respective stops, limit switch 9| will be carried into engagement with switching member 82 and thereby open limit switch 9| to interrupt the energizing circuit of the motor. It will be understood that the position of limit switch 9| relative to the rib 28 is adjustable so as to effect the opening of this limit switch when the desired positive twist of the blade I3 has been obtained.

This limit switch mechanism If the manual warp control switch 89 is now thrown out of engagement with contact 96 and into engagement with the opposite contact 94 an energizing 'circuit for operating motor 20 to reverse the warp or twist of the blade I3 will be established. This circuit may be traced from battery B through conductor |99, switch 90, contact 99, conductor |95, limit switch 99, conductor |91, the counter-clockwise rotation field winding |98 of motor 29, conductor it, the motor armature 29 and conductor |99 to battery B. In this case when motor 20 has operated to rotate the rib 29 in the counterclockwise direction suiiiciently to engage the successive ribs of the blade with their respective motion limit stops. then limit switch 99 will be operated into engagement with member 82 so as to open limit switch 99 and thereby interrupt the motor circuit. It will beunderstood that limit switch 99 is made adjustable relative to rib 28 so that it will ,be opened when the desired negative twist of the blade i3 has been obtained.

if now the manual Warp control switch 89 is returned into engagement with the middle contact 95, a circuit will be established for operating motor 29to return the rib 29 toits intermediate warp position in which it is shown in Fig. 4. This intermediate return circuit is under the automatic control of the resilient limit switch arms 95 and 85 which will be inabutting engagement due to the fact that the middle arm 85 is moved by the pin 61 into abutting engagement with Contact 8E whenever rib 28 is rotated in the counterclockwise direction from the position in which it is shown in Fig. 4. Thus whenever limit switch 99 is opened contact 95 always will be in engagement with contact 86. Consequently with limit switch 99 open when manual control switch 99 is returned to its mid-position a circuit is established from battery B through conductor 99, switch 89, contact 95, conductor |99, resilent contact arms 85 and 86, conductor |9 and hence through the clockwise rotation motor field winding |93, conductor |99, motor armature 29, conductor |95. The resulting clockwise operation of motor 29 will return rib 28 to its intermediate warp position as shown in Fig. 4 wherein ythe resilient switch arm 99 will disengage contact 86 to interrupt the motor circuit. Similarly when limit switch 9| is open and manual switch 99 is returned to its mid-position then the energizing circuit for motor 20 will extend through switch arms 85 and Bd, conductor and the counterclockwise rotation field winding |95 of motor 29.

. The resulting counter-clockwise operation of motor 29 will rotate rib 28 so as to reclose limit switch 9| before separating switch arm B5 from switch arm Sli when the intermediate warped i position is reached.

By means of the several improvements provided by the present invention, a powerful, accurate, and selective warping of the blade I3 between a predetermined intermediate position and desired positive and negative warp positions can be obtained. In both the positive and negative warp positions, the relative positions of the successive ribs in the blade are predetermined by the stops so as to provide the maximum aerodynamic eiiiciency. The intermediate warp position may be zero warp or a slight positive warp suitable for autogyration in case of engine failure.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An aircraft rotor having in combination a hub, a twistable blade having a main supporting spar fixed to the tip thereof and extending therethrough to provide a warp axis, said spar having articulated pivotal connections with said hub and means cooperating therewith for varying the pitch of said blades, and means including a reversible electric motor having a flexible shaft rotated thereby and gearing driven by said shaft and interconnected between said spar and the root of said blade for twisting said blade around said shaft to warp said blade to predetermined positive and negative warps relative to said tip.

2. A variable warp airfoil having in combination a main supporting spar, a series of ribs rotatably mounted on said spar, an airfoil envelope carried by said ribs with one end of said envelope iixed to one end of said spar, a pair of spaced apart warp control elements extending through and inter-connected with said ribs on opposite sides of said supporting spar, means for rotating the other end of said envelope relative to said spar to Warp said airfoil by the force of said warp control elements applied to said ribs and independently adjustable stop means for progressively interlocking said series of ribs with said supporting spar to progressively limit the rotation of said ribs in said series when said envelope is Warped.

3. In combination, a reversely variable pitch twistable arifoil blade, blade warping means including a reversible motor, flexible shaft driven by said motor, gearing means interconnected between said shaft and the root of said blade for twisting said blade, selective motor control means for energizing said motor to twist said blade to a predetermined positive warp, a predetermined negative warp, and a predetermined intermediate blade conformation, and pitch varying means separately controllable from said blade warping means.

4. A variable warp airfoil having in combination a twistable envelope having a slot extending through said airfoil envelope for permitting relative movement of opposite sides of said slot during the warping of said airfoil and guide means cooperating with said airfoil envelope for maintaining in predetermined alignment the sections of said airfoil envelope forming the opposite sides of said slot.

5. A variable warp airfoil having in combination a twistable envelope having a slot extending therethrough for permitting relative movement of said envelope on opposite sides of said slot during the warping of said airfoil, and interlocking sliding means within the structure of said airfoil and fastened to said envelope on opposite sides of said slot whereby opposite sides of said envelope remain in alignment and do not separate.

6. A variable warp airfoil having in combination a twistable envelope having in the trailing edge of said airfoil envelope a slot extending spanwise therethrough for permitting relative move-` ment of said envelope on opposite sides of said slot during the warping of said airfoil, said envelope containing interlocking parts forming the sides of said slot and being so shaped as to be capable of movement relative to each other in a spanwise direction but relatively incapable of separation from each other or movement out of alignment With each other.

7. A variable warp airfoil having a supporting spar longitudinally extendingV therethrough to provide a warp axis, a pair of spaced apart torsion elements each rigidlyinterconnected at one end with the tip of said spar and extending through said airfoil on opposite sides of said spar, means for rotating the opposite end of each torsion element in the same rotational direction relative to said spar thereby to warp said airfoil, and a series of independently adjustable warp limiting stop means connected between said torsion elements and said spar at longitudinally spaced points within said airfoil for limiting said warping to warp increments retrogressing from root to tip.

IGOR B. BENSEN.-

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,145,013 Gallaudet July 6, 1915 1,526,230 Pescara Feb. 10, 1925 1,611,717 Bushyager Dec. 21, 1926 2,407,185 Stalker Sept. 3, 1946 2,475,121 Avery July 5, 1949 FOREIGN PATENTS Number Country Date 15,207 Great Britain of 1911 272,578 Great Britain June 9, 1927 532,399 France Nov. 14, 1921 

